The homeostatic regulation of water balance is pivotal in mammalian survival. In this regard, the role of arginine vasopressin (AVP) in the renal regulation of water balance is well established; however several important questions remain which will be addressed in this program project grant (PPG). The adaptive responses whereby inner medullary collecting duct cells (IMCD), a major site of AVP activation of V2 receptors, survive in a hyperosmotic environment, which would fatally injure most mammalian cells, is a critical question whereby maximal urinary concentration occurs. Therefore a major focus of this PPG is to define the genomic and proteonomic repertoire in this hypertonic setting. As with the water channel response to hyperosmolality, the MAP kinase family (ERKs, JNKs and p38 MAP kinases) appears to be integral to the response of IMCD cells to an increase in extracellular osmolality. The role of c-JUN N-terminal kinase (JNK) appears to be critical in the survival of IMCD cells to hyperosmolalilty. Thus, studies using cells from mice genetically lacking JNK isoforms, as well as in vivo studies using JNK1 and 2 knockout mice will be undertaken to define the genes and proteins which are central to the survival of IMCD cells during hyperosmotic stress. Vascular smooth muscle cells (VSMC) are a particular focus of AVP via the V1a receptor. Thus, the AVP response to osmotic and non-osmotic stimuli in vivo can activate both V2 and V1 receptors. VSMC retain a degree of plasticity whereby changes in expression of muscle specific genes associated with disease can alter the capacity for proliferation, contraction and migration. Another focus of this PPG therefore is to define the molecular and cellular pathways whereby this phenotypic remodeling occurs in response to AVP and growth factors. Lastly, as has been the case during the entire duration of this PPG, experimental clinical models will be studied which can provide the basis for understanding disease mechanisms and also allow the translation of laboratory knowledge to patient-oriented research. The concept of the non-osmotic regulation of AVP and the pathways involved in body fluid volume regulation have emerged from this PPG in this manner. Using advanced molecular and cellular techniques, it is now possible to better understand defects in urinary concentration and dilution as will be studied in a section of this program project grant in experimental models of primary polydipsia, thyroid and adrenal disorders.